Screening for Drought Tolerance in Maize (Zea mays L.) Germplasm Using Germination and Seedling Traits under Simulated Drought Conditions

Genetic Potential of Newly Developed Maize Hybrids under Different Water-Availability Conditions in an Arid Environment

Drought is a crucial environmental stress that tremendously impacts maize production, particularly under abrupt climate changes. Consequently, breeding drought-tolerant and high-yielding maize hybrids has become decisive in sustaining its production and ensuring global food security under the global fast-growing population. The present study aimed to explore drought tolerance and agronomic performance of newly developed maize inbred lines and their hybrids. Ten newly developed maize inbred lines were crossed with two high-yielding testers using a line × tester mating design. The developed twenty hybrids alongside two high-yielding commercial hybrids were evaluated under water-deficit (5411 m3/ha) and well-watered (7990 m3/ha) conditions in dry summer climate conditions. Highly significant variations were detected among the evaluated hybrids for all studied agronomic traits under well-watered and water-deficit conditions. The inbred lines L10 and L6 were particularly notable, demonstrating the most significant negative general combining ability (GCA) effects for earliness, which is crucial for stress avoidance in both environmental settings. Inbred lines L11, L7, L6, and L1 also showed the highest positive and most significant GCA effects for key yield traits, indicating their potential as parents in breeding programs. The crosses L-10×T-1 and L-6×T-2 were outstanding for their heterotic effects on earliness in days to tasseling and silking. Similarly, the crosses L-4×T-2 and L-1×T-1 excelled in plant and ear heights under both irrigation regimes. The hybrids L-1×T-2 and L-7×T-1 demonstrated superior heterosis for chlorophyll content, number of rows per ear, and overall grain yield. Additionally, hybrids L-11×T-1 and L-11×T-2 exhibited remarkable heterotic effects for the number of grains per row, number of rows per ear, 100-kernel weight, and grain yield, highlighting their potential in breeding for productivity. Based on drought tolerance indices and cluster analysis, the cross combinations L-11×T-1, L-11×T-2, L-7×T-1, and L-1×T-2 were classified as the most drought-tolerant crosses. The principal component analysis highlighted traits such as days to tasseling, days to silking, chlorophyll content, plant height, ear height, number of grains per row, number of rows per ear, and 100-kernel weight can be taken as selection criteria for improving grain yield in maize breeding programs under limited water conditions. Based on the summarized results, the identified genetic materials could be considered promising under both conditions and hold potential for future breeding programs.

Rapid and low-cost screening for single and combined effects of drought and heat stress on the morpho-physiological traits of African eggplant (Solanum aethiopicum) germplasm

Drought and heat are two stresses that often occur together and may pose significant risks to crops in future climates. However, the combined effects of these two stressors have received less attention than single-stressor investigations. This study used a rapid and straightforward phenotyping method to quantify the variation in 128 African eggplant genotype responses to drought, heat, and the combined effects of heat and drought at the seedling stage. The study found that the morphophysiological traits varied significantly among the 128 eggplants, highlighting variation in response to abiotic stresses. Broad-sense heritability was high (> 0.60) for chlorophyll content, plant biomass and performance index, electrolyte leakage, and total leaf area. Positive and significant relationships existed between biomass and photosynthetic parameters, but a negative association existed between electrolyte leakage and morpho-physiological traits. The plants underwent more significant stress when drought and heat stress were imposed concurrently than under single stresses, with the impact of drought on the plants being more detrimental than heat. There were antagonistic effects on the morphophysiology of the eggplants when heat and drought stress were applied together. Resilient genotypes such as RV100503, RV100501, JAMBA, LOC3, RV100164, RV100169, LOC 3, RV100483, GH5155, RV100430, GH1087, GH1087*, RV100388, RV100387, RV100391 maintained high relative water content, low electrolyte leakage, high Fv/Fm ratio and performance index, and increased biomass production under abiotic stress conditions. The antagonistic interactions between heat and drought observed here may be retained or enhanced during several stress combinations typical of plants' environments and must be factored into efforts to develop climate change-resilient crops. This paper demonstrates improvised climate chambers for high throughput, reliable, rapid, and cost-effective screening for heat and drought and combined stress tolerance in plants.

Drought stress induced by polyethylene glycol (PEG) in local maize at the early seedling stage

Drought stress adversely impacts growth, crop production, reproductive organ development, and yield characteristics in maize. As a drought-sensitive crop, maize (Zea mays L.) shows considerable varietal differences. A study was conducted at the Tissue Culture Laboratory, Department of Biology, Faculty of Mathematics and Natural Sciences, University of North Sumatra, Medan, Indonesia in order to identify drought-tolerant maize varieties. During germination and early seedling growth, 16 local accessions were evaluated for drought tolerance. Based on local climate and soil conditions, these specific accessions were chosen. The varieties were tested against five levels of drought stress imposed by Polyethylene glycol 6000 (PEG-6000) at 10, 20, 30, 40, and 50%. An experiment with three replications was conducted using a completely randomized design. In the study, local maize accessions (BI3, SB5, DS2, and MN3) and the hybrid variety (H) showed the capability of tolerating drought stress. Generally, germination time, germination percent and vigor index, root and shoot length, shoot ratio, and fresh and dry weight were decreased by increasing PEG concentrations (up to 50%). According to ANOVA results, shoot water content was not significantly affected by the PEG, nor was the interaction between the PEG and the accessions. The root water content, however, was significantly affected by PEG, and the interaction between PEG and accessions. Although interactions between accessions with low PEG concentrations improved germination characteristics, the root histology of the accessions varied. According to drought tolerance indexes, five maize accessions are drought-tolerant, including H (0.683), SB5 (0.617), DS2 (0.565), MN3 (0.512), and BI3 (0.504). The drought-tolerant varieties are recommended in regions with low rainfall or low water sources since they are less water-intensive and produce higher yields.

Multivariate analysis compares and evaluates drought and flooding tolerances of maize germplasm

Drought and flooding are the two most important environmental factors limiting maize (Zea mays L.) production globally. This study aimed to investigate the physiological mechanisms and accurate evaluation indicators and methods of maize germplasm involved in drought and flooding stresses. The twice replicated pot experiments with 60 varieties, combined with the field validation experiment with 3 varieties, were conducted under well-watered, drought, and flooding conditions. Most varieties exhibited stronger tolerance to drought than flooding due to higher antioxidant enzyme activities, osmotic adjustment substances, and lower reactive oxygen species. In contrast, flooding stress resulted in higher levels of reactive oxygen species (particularly O2-), ascorbate peroxidase, catalase, peroxidase, and soluble sugars but lower levels of superoxide dismutase, proline, and soluble protein compared with well-watered conditions. Superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, proline, soluble sugars, and protein contents, in addition to plant height, leaf area/plant, and stem diameter, were accurate and representative indicators for evaluating maize tolerance to drought and flooding stresses and could determine a relatively high mean forecast accuracy of 100.0% for the comprehensive evaluation value. A total of 4 principal components were extracted, in which different principal components played a vital role in resisting different water stresses. Finally, the accuracy of the 3 varieties screened by multivariate analysis was verified in the field. This study provides insights into the different physiological mechanisms and accurate evaluation methods of maize germplasm involved in drought and flooding stresses, which could be valuable for further research and breeding.

Acetic acid positively modulates proline metabolism for mitigating PEG-mediated drought stress in Maize and Arabidopsis

Introduction

Osmotic imbalance is one of the major consequences of drought stress, negatively affecting plant growth and productivity. Acetic acid has modulatory roles in osmotic balance in plants; however, the mechanistic insights into acetic acid-mediated osmotic adjustment under drought stress remains largely unknown.

Methods

Here, we investigated how seed priming and seedling root treatment with acetic acid enabled maize plants overcoming polyethylene glycol (PEG)-induced drought effects.

Results

Maize seeds primed with acetic acid showed better growth performance when compared with unprimed seeds under PEG application. This growth performance was mainly attributed to improved growth traits, such as fresh weight, dry weight, length of shoots and roots, and several leaf spectral indices, including normalized difference vegetation index (NDVI) and chlorophyll absorption in reflectance index (MCARI). The levels of oxidative stress indicators hydrogen peroxide (H2O2) and malondialdehyde (MDA) did not alter significantly among the treatments, but proline content as well as the expression of proline biosynthetic gene, Δ1-PYRROLINE-5-CARBOXYLATE SYNTHETASE 1 (P5CS1) was significantly elevated in plants receiving acetic acid under PEG-treatments. On the other hand, treating the seedlings root with acetic acid led to a significant recovery of maize plants from drought-induced wilting. Although growth traits remained unchanged among the treatments, the enhancement of leaf water content, photosynthetic rate, proline level, expression of P5CS1, and antioxidant enzyme activities along with reduced level of H2O2 and MDA in acetic acid-supplemented drought plants indicated a positive regulatory role of acetic acid in maize tolerance to drought. Moreover, the high expression of P5CS1 and the subsequent elevation of proline level upon acetic acid application were further validated using wild type and proline biosynthetic mutant p5cs1 of Arabidopsis. Results showed that acetic acid application enabled wild type plants to maintain better phenotypic appearance and recovery from drought stress than p5cs1 plants, suggesting a crosstalk between acetic acid and proline metabolism in plants under drought stress.

Discussion

Our results highlight the molecular and intrinsic mechanisms of acetic acid conferring plant tolerance to drought stress.

Early selection for drought tolerance in popcorn based on gene effects estimated in seedlings

Low rainfall rates are becoming increasingly frequent because of climate change, causing droughts and threatening world food security. For popcorn, drought is the most limiting abiotic factor for plant's growth and development. Thus, the water deficit directly impacts for crop productivity. Based on knowledge of the genetic basis of traits involved in stages of popcorn germination and seedling development under water stress, genotypes with potential for adaptation to adverse growing conditions can be selected early. Therefore, data on genetic effects and combining ability of 10 popcorn parents were compiled to propose breeding strategies for the development of cultivars with greater adaptation to water stress in the early stages. Forty-five diallel hybrids were evaluated under two different water regimes, that is, water stress and full irrigation. This corresponded to a water retention capacity of 25% and 70% of the germination paper. The plants were watered daily as needed for seven days. A range of factors were evaluated, that is, germination traits including the germination speed index and germination on the seventh day; shoot traits including length and dry weight; and root system including length, dry weight, root-to-shoot ratio, maximum root number, root network area, specific and root network length, and root volume. Breeding for drought adaption in the early stages of popcorn development can be successful when hybrids are used, because of the genetic effects of dominance (ϕ_s). These control the traits evaluated at the seedling stage. The combinations L61 x P2 and L71 x P3 were recommended, in view of the more successful performance estimated for traits related to the shoot and root system.

Root plasticity: an effective selection technique for identification of drought tolerant maize (Zea mays L.) inbred lines

The decline in tropical maize productivity due to climatic vulnerability is a matter of serious concern as being a food and feed/fodder commodity, it is an important crop for the sustenance of human life. Genetic selections and development of water deficit stress (WDS) tolerant commercial varieties have potential to offset the impact of changing temperatures and precipitation. For trait-specific genetic enhancement, there is a need to understand a suite of adaptation strategies for crop. We studied the response of various shoot and root traits in 71 maize inbreds of diverse origin under simulated sub-optimal water supply controlled conditions, delineated an array of traits which must be considered for selection for WDS and validated the inbreds harbouring tolerance to WDS for selection of authentic donor lines to develop WDS tolerant hybrids. A large data set was limited to uncorrelated traits based on principal component analysis and variability among maize lines was deciphered using heatmap dendrogram. We also reported the relevance of root anatomical plasticity to the inherent potential of lines to combat WDS. We recommend incorporating the changes in number and diameter of xylem and metaxylem under simulated controlled conditions as a part of precise phenotyping for WDS in maize. The study led to identification of WDS tolerant line LM22 in maize.

Transcriptome analysis of drought-responsive and drought-tolerant mechanisms in maize leaves under drought stress

Maize is a major crop essential for food and feed, but its production is threatened by various biotic and abiotic stresses. Drought is one of the most common abiotic stresses, causing severe crop yield reduction. Although several studies have been devoted to selecting drought-tolerant maize lines and detecting the drought-responsive mechanism of maize, the transcriptomic differences between drought-tolerant and drought-susceptible maize lines are still largely unknown. In our study, RNA-seq was performed on leaves of the drought-tolerant line W9706 and the drought-susceptible line B73 after drought treatment. We identified 3147 differentially expressed genes (DEGs) between these two lines. The upregulated DEGs in W9706 were enriched in specific processes, including ABA signaling, wax biosynthesis, CHO metabolism, signal transduction and brassinosteroid biosynthesis-related processes, while the downregulated DEGs were enriched in specific processes, such as stomatal movement. Altogether, transcriptomic analysis suggests that the different drought resistances were correlated with the differential expression of genes, while the drought tolerance of W9706 is due to the more rapid response to stimulus, higher water retention capacity and stable cellular environment under water deficit conditions.

Impact of climate perturbations on seeds and seed quality for global agriculture

In agriculture, seeds are the most basic and vital input on which croplands productivity depends. These implies a good starting material, good production lines and good storage options. High-quality seed lots must be free of pests and pathogens and contain a required degree of genetic purity. Seeds need also to be stored in good condition between harvest and later sowing, to insure later on the field a good plant density and higher crop yield. In general, these parameters are already widely accepted and considered in many countries where advanced technologies evaluate them. However, the more and more frequently devastating climate changes observed around the world has put seed quality under threat, and current seeds may not be adapted to hazardous and unpredictable conditions. Climate-related factors such as temperature and water availability directly affect seed development and later germination. For these reasons, investigating seed quality in response to climate changes is a step to propose new crop varieties and practices that will bring solutions for our future.

Combining ability and testcross performance of multi-nutrient maize under stress and non-stress environments

While significant progress has been made by several international breeding institutions in improving maize nutritional quality, stacking of nutritional traits like zinc (Zn), quality protein, and provitamin A has not received much attention. In this study, 11 newly introduced Zn-enhanced inbred lines were inter-mated with seven testers from normal, provitamin A and quality protein maize (QPM) nutritional backgrounds in order to estimate the general combining ability (GCA) and specific combining ability (SCA) for grain yield (GY) and secondary traits under stress conditions [(combined heat and drought stress (HMDS) and managed low nitrogen (LN)] and non-stress conditions [(summer rainfed; OPT) and well-watered (irrigated winter; WW)] in Zimbabwe. Lines L6 and L7 had positive GCA effects for GY and secondary traits under OPT and LN conditions, and L8 and L9 were good general combiners for GY under HMDS conditions. Superior hybrids with high GY and desirable secondary traits were identified as L10/T7 and L9/T7 (Zn x normal), L2/T4, L4/T4, L3/T5 (Zn x provitamin A), and L8/T6 and L11/T3 (Zn x QPM), suggesting the possibility of developing Zn-enhanced hybrids with high yield potential using different nutritional backgrounds. Both additive and dominance gene effects were important in controlling most of the measured traits. This suggests that selecting for desirable traits during inbred line development followed by hybridization and testing of specific crosses under different management conditions could optimize the breeding strategy for stacked nutritionally-enhanced maize genotypes.

The Physiological Responses of Wheat and Maize Seedlings Grown under Water Deficit Are Modulated by Pre-Application of Auxin-Type Plant Growth Regulators

The physiological responses of wheat and maize seedlings to exogenous auxin-type compounds 1-[2-chloroethoxycarbonyl-methyl]-4-naphthalenesulfonic acid calcium salt (TA-12) and 1-[2-dimethylaminoethoxicarbonylmethyl]naphthalene chlormethylate (TA-14) application prior to polyethyleneglycol-6000 (PEG) treatment were studied. PEG treatment inhibited seedlings growth and caused alterations in their antioxidant defence which was crop-specific. PEG increased the non-enzymatic antioxidants along with inhibition of enzymatic antioxidant activity in wheat, while in maize the opposite effects were found. The TA-12 and TA-14 applied alone increased most of the growth parameters measured in both crops, as well as the catalase activity and protein content of wheat. The growth of PEG-treated wheat and maize plants was improved by foliar spray with TA-compounds (TAs). Application of TAs before PEG treatment maintained low-molecular weight thiol-containing compounds and protein contents, and catalase and peroxidase activities close to the control levels. This was better expressed in maize than in wheat seedlings. The results showed that the preliminary application of TA-12 and TA-14 can reduce the adverse effects of moderate water deficit by crop-specific adjustment of the antioxidant defence to counteract stress.

Analysis of Physiological Indicators Associated with Drought Tolerance in Wheat under Drought and Re-Watering Conditions

Wheat (Triticum aestivum L.) production is severely threatened by an increase in the frequency of drought events. It is crucial to determine stable and effective morphological, physiological, and associated oxidative stress indicators, to evaluate the drought tolerance of wheat for breeding and cultivation. Therefore, the cultivars Luohan 22 (LH 22, drought-tolerant) and Zhengmai 366 (ZM 366, drought-sensitive) were used as experimental materials to analyze the changes in 12 physiological and biochemical indicators, as well as the yield, when the stress was prolonged to different times. Re-watering after 6 days of drought can effectively alleviate the associated oxidative stress of drought to wheat. The physiological responses of plants were reversible when they were re-watered in the range of 6 to 12 days after drought. The degree of recovery of LH 22 was higher than that of ZM 366. Afterwards, seven indicators, including stomatal conductance, proline, malondialdehyde, soluble sugar, hexokinase, glucose, and the non-photochemical quenching parameter, were screened out to characterize tolerance of wheat to drought using the multivariate statistical analytical method. This study further investigated the method of evaluating and indexing tolerance of wheat to drought, from the physiological and biochemical levels. This study can provide a theoretical basis and reference for the selection of wheat cultivars to breed and cultivate against drought stress.

Dry Matter Yield Stability Analysis of Maize Genotypes Grown in Al Toxic and Optimum Controlled Environments

Breeding for Al tolerance is the most sustainable strategy to reduce yield losses caused by Al toxicity in plants. The use of rapid, cheap and reliable testing methods and environments enables breeders to make quick selection decisions. The objectives of this study were to (i) identify high dry matter yielding and stable quality protein maize (QPM) lines grown under Al toxic and optimum conditions and (ii) compare the discriminating power of laboratory- and greenhouse-based testing environments. A total of 75 tropical QPM inbred lines were tested at seedling stage for dry matter yield and stability under optimum and Al toxic growing conditions across six laboratory- and greenhouse-based environments. The nutrient solution method was used for the laboratory trials, while the soil bioassay method was used for the greenhouse trials. A yield loss of 55% due to Al toxicity was observed, confirming the adverse effects of Al toxicity on maize productivity. The ANOVA revealed the presence of genetic variation among the set of genotypes used in this study, which can be exploited through plant breeding. Seventeen stable and high-yielding lines were identified and recommended. Greenhouse-based environments were more discriminating than laboratory environments. Therefore, we concluded that greenhouse environments are more informative than laboratory environments when testing genotypes for Al tolerance.

Phenotypic and transcriptomic responses of cultivated sunflower seedlings (Helianthus annuus L.) to four abiotic stresses

Plants encounter and respond to numerous abiotic stresses during their lifetimes. These stresses are often related and could therefore elicit related responses. There are, however, relatively few detailed comparisons between multiple different stresses at the molecular level. Here, we investigated the phenotypic and transcriptomic response of cultivated sunflower (Helianthus annuus L.) seedlings to three water-related stresses (i.e., dry-down, an osmotic challenge, and salt stress), as well as a generalized low-nutrient stress. All four stresses negatively impacted seedling growth, with the nutrient stress having a more divergent response from control as compared to the water-related stresses. Phenotypic responses were consistent with expectations for growth in low-resource environments, including increased (i.e., less negative) carbon fractionation values and leaf C:N ratios, as well as increased belowground biomass allocation. The number of differentially expressed genes (DEGs) under stress was greater in leaf tissue, but roots exhibited a higher proportion of DEGs unique to individual stresses. Overall, the three water-related stresses had a more similar transcriptomic response to each other vs. nutrient stress, though this pattern was more pronounced in root vs. leaf tissue. In contrast to our DEG analyses, co-expression network analysis revealed that there was little indication of a shared response between the four stresses in despite the majority of DEGs being shared between multiple stresses. Importantly, osmotic stress, which is often used to simulate drought stress in experimental settings, had little transcriptomic resemblance to true water limitation (i.e., dry-down) in our study, calling into question its utility as a means for simulating drought.

Effects of Different Drought Degrees on Physiological Characteristics and Endogenous Hormones of Soybean

Drought affects crop developmentnand growth. To explore the physiological effects of drought stress on soybean, HeiNong44 (HN44) and HeiNong65 (HN65) varieties were used as experimental materials and PEG-6000 was used as the osmotic medium. The antioxidant enzyme activity, osmotic adjustment substance content, antioxidant capacity, and endogenous hormone content of the two soybean varieties were studied under different drought degrees and different treatment durations. Drought stress caused significant physiological changes in soybean. The antioxidant enzyme activities, osmoregulation substance content, and total antioxidant capacity (T-AOC) of HN65 and HN44 showed an increasing trend under mild and moderate drought, however, they first increased and then decreased under severe drought conditions. Following the extension of treatment time, malondialdehyde (MDA) showed an increasing trend. As drought increased, gibberellin (GA) content showed a decreasing trend, while abscisic acid (ABA), salicylic acid (SA), and zeatin nucleoside (ZA) content showed an increasing trend. The auxin (IAA) content of the two varieties showed opposite change trends. In short, drought had a significant impact on the physiology of these two soybean varieties; however, overall, the drought resistance of HN65 was lower than that of HN44. This study provides a research theoretical basis for addressing the drought resistance mechanism and the breeding of drought resistant soybean varieties.

Physio-morphological traits and osmoregulation strategies of hybrid maize (Zea mays) at the seedling stage in response to water-deficit stress

Drought has been identified as a major factor restricting maize productivity worldwide, especially in the rainfed areas. The objective of the present study was to investigate the physiological adaptation strategies and sugar-related gene expression levels in three maize (Zea mays L.) genotypes with different drought tolerance abilities (Suwan4452, drought tolerant as a positive check; S7328, drought susceptible as a negative check; Pac339, drought susceptible) at the seedling stage. Ten-day old seedlings of maize genotypes were subjected to (i) well-watered (WW) or control and (ii) water-deficit (WD) conditions. Leaf osmotic potential of cv. S7328 under WD was significantly decreased by 1.35-1.45 folds compared with cv. Pac339 under WW, whereas it was retained in cv. Suwan4452, which utilized total soluble sugars as the major osmolytes for maintaining leaf greenness, F_v/F_m, Φ_PSII, and stomatal function (P_n, net photosynthetic rate; g_s, stomatal conductance; and E, transpiration rate). Interestingly, sucrose degradation (65% over the control) in cv. Pac339 under WD was evident in relation to the downregulation of the ZmSPS1 level, whereas glucose enrichment (1.65 folds over the control) was observed in relation to the upregulation of ZmSPS1 and ZmSUS1. Moreover, CWSI (crop water stress index), calculated from leaf temperature of stressed plants, was negatively correlated with E, g_s, and P_n. Overall, growth characteristics, aboveground and belowground parts, in the drought-susceptible cv. Pac339 and cv. S7328, were significantly decreased (> 25% over the control), whereas these parameters in the drought-tolerant cv. Suwan4452 were unaffected. The study validates the use of leaf temperature, CWSI, P_n, g_s, and E as sensitive parameters and overall growth characters as effective indices for drought tolerance screening in maize genotypes at the seedling stage. However, further experiments are required to validate the results observed in this study under field conditions.

Optimizing sowing window, cultivar choice, and plant density to boost maize yield under RCP8.5 climate scenario of CMIP5

The impacts of climate change and possible adaptations to food security are a global concern and need greater focus in arid and semi-arid regions. It includes scenario of Coupled Model Intercomparison Phase 5 (CMIP-RCP8.5). For this purpose, two DSSAT maize models (CSM-CERES and CSM-IXIM) were calibrated and tested with two different maize cultivars namely Single Cross 10 (SC10) and Three Way Cross 324 (TW24) using a dataset of three growing seasons in Nile Delta. SC10 is a long-growing cultivar that is resistant to abiotic stresses, whereas TW24 is short and sensitive to such harsh conditions. The calibrated models were then employed to predict maize yield in baseline (1981-2010) and under future time slices (2030s, 2050s, and 2080s) using three Global Climate Models (GCMs) under CMIP5-RCP8.5 scenario. In addition, the use of various adaptation options as shifting planting date, increasing sowing density, and genotypes was included in crop models. Simulation analysis showed that, averaged over three GCMs and two crop models, the yield of late maturity cultivar (SC10) decreased by 4.1, 17.2, and 55.9% for the three time slices of 2030s, 2050s, and 2080s, respectively, compared to baseline yield (1981-2010). Such reduction increased with early maturity cultivar (TW24), recording 12.4, 40.6, and 71.3% for near (2030s), mid (2050s), and late century (2080s) respectively relative to baseline yield. The most suitable adaptation options included choosing a stress-resistant genotype, changing the planting date to plus or minus 30 days from baseline planting date, and raising the sowing density to 9 m^-2 plants. These insights could minimize the potential reduction of climate change-induced yields by 39% by late century.

Variation in Maize Grain Yield Indices When Exposed to Combined Heat and Water Stress Conditions under Different Soil Amendments

Increased yield can be achieved by optimising the growth environment, improving the plant gene pool, or a combination of the two. This study’s objective was to evaluate the effect of combined heat and water stress (CHWS) on maize yield, grown in various soil conditions. The experimental design was a four-replicated 3 × 3 × 2 × 3 factorial in a completely randomized design. Three water stress levels, three soil amendments, two soil textural types, and three drought-tolerant maize varieties were combined to create 54 treatment interactions. The result showed that as the severity of the water stress increased, the yield decreased. The near terminal water stress reduced cob weight, grain weight, and grain number by 96, 97, and 97%, respectively. The maize varieties were ranked WE5323 ≥ ZM1523 > WE3128 in terms of average performance and stability. Under heat and moderate water stress, the poultry manure amendment performed well for WE5323 and ZM1523, while the mineral fertilizer amendment performed best for WE3128. Compared to the inorganic amendment, the organic had a greater ameliorative capacity for grain yield under CHWS. For improved grain yield under CHWS, farmers are advised to grow WE5323 and ZM1523 with organic amendments. The findings in this study could improve food security strategies for low-income households living in high-stress environments.

Fertigation with Zn-Lysine Confers Better Photosynthetic Efficiency and Yield in Water Stressed Maize: Water Relations, Antioxidative Defense Mechanism and Nutrient Acquisition

Different strategies including the exogenous use of micronutrient-chelated amino acids are being employed for better crop yield with limited fresh water for irrigation. The present study was conducted to assess the effects of foliar-applied Zn-lysine (Zn-Lys) on maize growth and yield under limited irrigation, in relation to physio-biochemical mechanisms such as the plant–water relations, photosynthetic efficiency, antioxidant defense mechanism, amino acid accumulation and nutrient acquisition. The experiment comprised two maize cultivars (MMRI and Pearl), two irrigation levels and three levels of Zn-Lys (0.25, 0.5 and 0.75%). Zn-Lys fertigation was found to be effective in reducing the negative impacts of limited water supply on grain yield, associated with improved photosynthetic efficiency, water relations, antioxidative defense mechanism and reduced lipid peroxidation in both maize cultivars. Zn-Lys-induced improvement in antioxidative mechanisms was associated with improved content of non-enzymatic antioxidants and activities of antioxidant enzymes. Foliar-fertigation with Zn-Lys also significantly improved the contents of various amino acids including Lys, as well as uptake of nutrients in both maize cultivars. In conclusion, the 0.5% level of Zn-Lys was found to be effective in ameliorating the negative impacts of water stress for better grain yield in both maize cultivars that can also be used as an important environment-friendly source of Zn to fulfill maize Zn deficiency.

Submergence Gene Sub1A Transfer into Drought-Tolerant japonica Rice DT3 Using Marker-Assisted Selection

Flash flooding is a major environmental stressor affecting rice production worldwide. DT3 is a drought-tolerant, recurrent parent with a good yield, edible quality, and agronomic traits akin to those of an elite Taiwanese variety, Taiken9 (TK9). Progenies carrying Sub1A can enhance submergence stress tolerance and can be selected using the marker-assisted backcross (MAB) breeding method. For foreground selection, Sub1A and SubAB1 were utilized as markers on the BC₂F₁, BC₃F₁, and BC₃F₂ generations to select the submergence-tolerant gene, Sub1A. Background selection was performed in the Sub1A-BC₃F₂ genotypes, and the percentages of recurrent parent recovery within individuals ranged from 84.7–99.55%. BC₃F₃ genotypes (N = 100) were evaluated for agronomic traits, yield, and eating quality. Four of the eleven BC₃F₄ lines showed good yield, yield component, grain, and eating quality. Four BC₃F₄ lines, SU39, SU40, SU89, and SU92, exhibited desirable agronomic traits, including grain quality and palatability, consistent with those of DT3. These genotypes displayed a high survival rate between 92 and 96%, much better compared with DT3 with 64%, and demonstrated better drought tolerance compared to IR64 and IR96321-345-240. This study provides an efficient and precise MAB strategy for developing climate-resilient rice varieties with good grain quality for flood-prone regions.

Genetics of Germination and Seedling Traits under Drought Stress in a MAGIC Population of Maize

Drought is one of the most detrimental abiotic stresses hampering seed germination, development, and productivity. Maize is more sensitive to drought than other cereals, especially at seedling stage. Our objective was to study genetic regulation of drought tolerance at germination and during seedling growth in maize. We evaluated 420 RIL with their parents from a multi-parent advanced generation inter-cross (MAGIC) population with PEG-induced drought at germination and seedling establishment. A genome-wide association study (GWAS) was carried out to identify genomic regions associated with drought tolerance. GWAS identified 28 and 16 SNPs significantly associated with germination and seedling traits under stress and well-watered conditions, respectively. Among the SNPs detected, two SNPs had significant associations with several traits with high positive correlations, suggesting a pleiotropic genetic control. Other SNPs were located in regions that harbored major QTLs in previous studies, and co-located with QTLs for cold tolerance previously published for this MAGIC population. The genomic regions comprised several candidate genes related to stresses and plant development. These included numerous drought-responsive genes and transcription factors implicated in germination, seedling traits, and drought tolerance. The current analyses provide information and tools for subsequent studies and breeding programs for improving drought tolerance.

Genetic diversity of a global collection of maize genetic resources in relation to their subspecies assignments, geographic origin, and drought tolerance

The genetic diversity among an international collection of 40 maize accessions has been evaluated using DNA ISSR fingerprinting. Among the 180 ISSR markers scored by 15 primers, 161 markers (89.59%) were polymorphic and 19 were unique in 16 accessions. A cluster tree based on the average distance coefficients and the Dice similarity indices divided the accessions into three major groups, each including clusters of accessions assigned to their subspecies. However, a low level of genetic differentiation among the accessions was demonstrated by the STRUCTURE analysis of ISSR data in agreement with the low gene flow (Nm) value among the accessions. A scatter diagram of the principal component analysis (PCA) based on ISSR data analysis revealed that the accessions were differentiated into three groups comparable to those produced by the cluster analysis, in which some accessions of the same subspecies showed a close similarity to each other. A scatter diagram of the principal coordinate analysis (PCoA) based on the drought tolerance indices (DTIs) showed that nine genetically similar accessions share drought tolerance characteristics; these include four of subsp. indurata, three of subsp. everata, and two of subsp. indentata. An abundance of unique ISSR alleles found in the 16 accessions, including the nine drought-tolerant accessions, represents rich untapped genetic resources and these accessions may be exploited in the future breeding of maize commercial lines.

Screening and identification of abiotic stress-responsive efficient antifungal Pseudomonas spp. from rice rhizospheric soil

Plant growth-promoting rhizobacteria (PGPR) are a collection of microorganisms often used to support and promote plant development and combat plant infectious diseases with various biological control methods. The most significant restricting factors for agricultural productivity worldwide are abiotic constraints. In the present study, seven bacterial isolates from the rice rhizosphere were selected for detailed tests based on results obtained in experiments determining the ACC deaminase synthesis and drought tolerance at -0.30 MPa PEG level. Screening results of the stress tolerance analysis of the seven isolates for elevated temperature (50°C), alkalinity (10% NaCl), and drought (-1.2 MPa) showed that abiotic stress resistance was less prevalent in DRO2, DRO13, and DRO43 isolates than in DRO17, DRO28, DRO35, and DRO51 isolates. During the study, it was observed that DRO17, DRO28, and DRO51 tended to maintain similar cell density at -0.73 MPa PEG level, as observed at -0.30 MPa stress condition. No bacterial growth was observed at higher PEG level (-1.12 MPa) for any bacterial isolate. Four strains of Pseudomonas (DRO17, DRO28, DRO35, and DRO51) exhibited salinity and temperature tolerance. Antifungal screening using the bangle method showed that DRO35 was highly antagonistic towards Rhizoctonia solani 4633, followed by Fusarium moniliforme 4223, with an inhibition of 64.3% and 48%, respectively. The DRO28 isolate exhibited 72.5% growth inhibition for Fusarium moniliforme 4223, while the DRO51 isolate showed 38.2% growth inhibition for Bipolaris hawaiiensis 2445. DRO17 reduced the growth of Rhizoctonia solani 4633, and Curvularia lunata 350 by 36% and 31%, respectively. In conclusion, the screening of bacterial strains with promising stress tolerance and antifungal characteristics could support farmers to achieve the required positive outcomes in the agriculture field.

Physiological, Biochemical and Yield-Component Responses of Solanum tuberosum L. Group Phureja Genotypes to a Water Deficit

Water deficits are the major constraint in some potato-growing areas of the world. The effect is most severe at the tuberization stage, resulting in lower yield. Therefore, an assessment of genetic and phenotypic variations resulting from water deficits in Colombia germplasm is required to accelerate breeding efforts. Phenotypic variations in response to a water deficit were studied in a collection of Solanum tuberosum Group Phureja. A progressive water deficit experiment on the tuberization stage was undertaken using 104 genotypes belonging to the Working Collection of the Potato Breeding Program at the Universidad Nacional de Colombia. The response to water deficit conditions was assessed with the relative chlorophyll content (CC), maximum quantum efficiency of PSII (F_v/F_m), relative water content (RWC), leaf sugar content, tuber number per plant (TN) and tuber fresh weight per plant (TW). Principal Component Analysis (PCA) and cluster analysis were used, and the Drought Tolerance Index (DTI) was calculated for the variables and genotypes. The soluble sugar contents increased significantly under the deficit conditions in the leaves, with a weak correlation with yield under both water treatments. The PCA results revealed that the physiological, biochemical and yield-component variables had broad variation, while the yield-component variables more powerfully distinguished between the tolerant and susceptible genotypes than the physiological and biochemical variables. The PCA and cluster analysis based on the DTI revealed different levels of water deficit tolerance for the 104 genotypes. These results provide a foundation for future research directed at understanding the molecular mechanisms underlying potato tolerance to water deficits.

Morpho-physiological and biochemical changes in finger millet [Eleusine coracana (L.) Gaertn.] under drought stress

Finger millet (Eleusine coracana L. Gaertn.) is a nutritious and climate-resilient crop with a C₄ type carbon fixation pathway. The present study was aimed to assess the drought tolerance capacities of four finger millet genotypes based on their physiological and biochemical characteristics at three different phenological stages. Finger millet genotypes RAU 8, GPU 67, GPU 28 and MS 9272 were subjected to two water regimes, regular irrigation (control) and suspended irrigation (drought stress). During water regimes, morpho-physiological [biomass accumulation, leaf relative water content, and photosynthetic pigments] and biochemical changes [proline content, water soluble carbohydrates, antioxidant enzymes, and malondialdehyde content] were studied during seedling (18th day), vegetative (49th day) and early flowering stages (73rd day). The maintenance of growth especially root growth, biomass accumulation, the differential response in the concentration and changes of pigments, accumulation of proline, water-soluble carbohydrates and increased levels of antioxidant enzymes under drought stress play a major role in differential tolerance in finger millet genotypes that is conferred by the biplot analysis. The genotype RAU 8 is the most drought-tolerant genotype at all the three different phenological stages. Whereas the genotype GPU 67 was identified as sensitive at the seedling stage and its tolerance level was improved at vegetative and early flowering stages. The genotypes GPU 28 and MS 9272 were considered as drought sensitive at all three different phenological stages. Our results provide inputs to the breeders to select genotypes as parents and to design effective strategies in crop improvement programs.